Design of Artificial Knee Joint

7/23/2019 Design of Artificial Knee Joint

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1

DESIGN OF ARTIFICIAL KNEE JOINT

In this project, our aim is to design and analyze a mechanism to support the human knee

during the weight acceptance part of the gait cycle by taking half of the maximum load and

provide free motion for the rest of the cycle. The basic functioning of the knee was studied and

the anatomy and mechanism of walking were analysed for this purpose.

Then based on the data gathered, a system based on a torsion spring controlled by a

Whitworth uick !eturn "echanism was proposed. The Whitworth mechanism was driven by a

motor which was controlled by a microcontroller#sensor system. The specifications of the motor

were based on the tor$ue re$uirement results of the dynamic analysis in %olidworks &'(& and the

speed calculations were made analytically based on the human walking pattern.

)ased on the gait cycle, the velocity ratio was decided and the link lengths were calculated

for the mechanism analytically. The entire system was made into %olidworks &'(& and the

dynamic analysis of the system were done including the force analysis, Tor$ue re$uirements on

the motor and the variation of these $uantities with respect to the time of operation of the system.

*ecessary analyses were also done in the software itself to ensure that the Whitworth mechanism

can withstand the maximum load of +' *.m with a good fatigue life during its period of

operation.


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2

Table Of Contents

Sr.

No.

Chapter Name Pae

No.

! bstract (

! -ist of igures / Tables 0

! *omenclature 1

" Introduction

(.( 2steoarthritis

3

4

# -iterature !eview

&.( Walking "echanism

&.(.( 5ait 6hases &.(.& natomical terms of motion

&.(.&.( lexion and extension

&.(.&.& bduction and dduction

&.(.&.+ 7levation and depression

&.(.&.0 !otation

&.& nalysis of 8nee 9oint

&.&.( :egrees of reedom

&.&.& uasi#%tiffness of 8nee

&.&.+ -oad constraints on the knee

&.+ 2rthotics

&.+.( Types of 7xoskeletons

;

;

;arious %tances of 5ait =ycle ;

&.& >arious "otion Terms ('

&.+ 8nee joint showing the cartilage and the meniscus ((

&.0 >arious dimensional motions of 8nee (+

&.1 "oment#ngle 5raph (+&.3 6arallel type 7xoskeleton (4

&.4 %eries type 7xoskeleton (;

+.( -ower 7xtremity -imbs (w A Working %troke >elocity Bm?sC

3. >r A !eturn %troke >elocity Bm?sC

4. a A "oment when heel strikes the ground B*.mC

;. b A "aximum moment at an angle of (1 degree B*.mC


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C+APTER "

INTROD,CTION

The knee is a hinge#like joint, and is a place where bones come together in the body to

facilitate movement and bear weight.

The knee joint connects the upper and lower portions of the leg and allows it to bend and

straighten # and even rotate inward and outward a little bit. It is made up of four bones, the

largest being the femur Bthigh boneC and the tibia Blarge shin boneC, which go head#to#head

within the knee joint and bear the brunt of the impact of movement.

The smaller two are the fibula Bsmaller shin boneC, which sits to the side of and slightly under

the tibia, and the patella Bknee capC, which acts like a shield to protect the knee joint from

trauma. %everal muscles, tendons and ligaments connect these four bones, make movement

possible, and help keep the knee joint aligned and stable.

ig (.(D The anatomy of knee showing the joints connecting the two major

bones E emur and tibia and the two smaller bonesD 6atella and ibula F&&G


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"." Osteoarthr(t(s

2steoarthritis B2C is one of the most common forms of arthritis. It is a chronic condition in

which the material that cushions the joints, called cartilage, breaks down. This causes the bones

to rub against each other, causing stiffness, pain and loss of joint movement. The cause is not

fully understood.

"ore than &' million people in the H% suffer from knee osteoarthritis B2C. )y &'+', &'@

of mericans Babout 4' million peopleC of more than 31 years of age are at risk for 2. 5lobal

statistics reveal over ('' million people worldwide suffer from 2, which is one of the most

common causes of disability. In addition, younger individuals may be susceptible to injury#

induced 2. "ore than 1'@ of the population around the world Bmore than 31 yearsC show #

ray evidence of 2 in one of the joints, thus demonstrating the high incidence of this disease.

While 2 is e$ually present in men and women, it appears to be more common among younger

men Bless than 01 yearsC and in the older women Bmore than 01 yearsC.

s per a recent report published in the Times of India B&'('C regarding 2, over 0'@ of the

Indian population in the age group of 4' years or above suffer from 2. *early &@ of these

undergo severe knee pain and disability. s per a recent statement $uoted by 6iramal Jealthcare

-imited in a nationwide campaign against chronic diseases, KIndia is expected to be the chronic

disease capital, with 3' million people with arthritis, by &'&1. The government, the private

sector, the medical fraternity and *52s should come together against the onslaught of chronic

diseases.L lso, majority of those suffering from 2 are deprived of access to $uality treatment.

2ur attempt in this paper is to make a mechanism which morphs its stiffness according to the

increasing and decreasing re$uirements during the gait cycle of humans. The mechanism should

provide the maximum stiffness when the knee is undergoing the maximum weight acceptance

and should provide complete freedom to move the knees when the knee is not taking any load.


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C+APTER #

LITERAT,RE RE-IE

#." al/(n 0e*han(sm

Walking is done in a double pendulum mechanism. Juman walking is accomplished with a

strategy called the double pendulum. :uring forward motion, the leg that leaves the ground

swings forward from the hip. This sweep is the first pendulum. Then the leg strikes the ground

with the heel and rolls through to the toe in a motion described as an inverted pendulum. The

motion of the two legs is coordinated so that one foot or the other is always in contact with the

ground.

#."." Ga(t Phases

gait cycle is defined as the period between two consecutive heel strikes of the same foot

with the ground, and is composed of a stance phase where the foot is on the ground and a swingphase where the foot is off the ground, as schematically shown. The stance phase comprises a

Weight cceptance Bfirst 0'@C and a terminal stance B 0'E3+@C sub#phases. The human knee

demonstrates a linear flexion stage and a linear extension stage in the W phase of the gait for

normal, level#ground walking. %tance phase begins with the heel strike # this is the moment when

the heel begins to touch the ground but the toes do not yet touch. In the mid#stance phase, we can

ig. &.(D >arious %tances of 5ait =ycle F&+G


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see settlement of the foot at the lateral border. The toe#off phase is also named the propulsive

phase.

When the stance phase ends, the swing phase begins. This phase is the phase between the toe

off phase and the heel strike phase. In the swing phase we can recognize two extra phases #

acceleration and declaration. The acceleration phase goes from toe#off to mid#swing, while

declaration goes from mid#swing to heel strike. In the acceleration phase, the swing leg makes an

accelerated forward movement with the goal of propelling the body weight forward. The

declaration phase brakes the velocity of this forward body movement in order to place your foot

down with control. )etween these two phases, the mid#swing phase occurs. In this phase, both

feet are under the body, with the heel next to each other.

6articularly, we studied the effect of body size and gait speed on the knee moment#angle

performance of subjects with gait speed of (.'(E&.3+ m?s, body height of (.0+E(.;3 m, and body

weight of 13.'E


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7xtension is the opposite of flexion,

describing a straightening movement that increases theangle between body parts. When a joint

can move forward and backward, such as the neck and trunk, extension refers to movement in

the posterior direction. or example, when standing up, the knees are extended. 7xtension of the

hip or shoulder moves the arm or leg backward. When the chin is against the chest, the head is

flexed, and the trunk is flexed when a person leans forward.


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#.".#.# Ab2)*t(on an2 A22)*t(on

bduction refers to a motion that pulls a structure or part away from the midline of the body.

In the case of fingers and toes, it refers to spreading the digits apart, away from the centerline of

the hand or foot. bduction of the wrist is also called radial deviation. or example, raising the

arms up, such as when tightrope#walking, is an example of abduction at the shoulder. When thelegs are splayed at the hip, such as when doing a star jump or doing a split, the legs are abducted

at the hip.

dduction refers to a motion that pulls a structure or part toward the midline of the body, or

towards the midline of a limb. In the case of fingers and toes, it refers to bringing the digits

together, towards the centerline of the hand or foot. dduction of the wrist is also called ulnar

deviation. or example, dropping the arms to the sides, or bringing the knees together, are

examples of adduction.

#.".#.$ Ele3at(on an2 2epress(on

The terms elevation and depression refer to movement above and below the horizontal. They

derive from the -atin terms with the same meaning. 7levation refers to movement in a superior

direction. or example, shrugging is an example of elevation of the scapula. :epression refers to

movement in an inferior direction, the opposite of elevation.

#.".#.% Rotat(on

!otation of body parts is referred to as internal or external, referring to rotation towards or

away from the center of the body. Internal rotation Bor medial rotationC refers to rotation towards

ig. &.&D >arious "otion Terms F&0G


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the axis of the body. 7xternal rotation Bor lateral rotationC refers to rotation away from the center

of the body

#.# Anal4s(s of Knee Jo(nt

lthough the leg bones join together at the knee, they donNt actually touch each otherD they are

held slightly apart by cartilage, a rubbery, gel#like tissue that sits on the ends of bones like plush

slippers on your feet. =artilage, which is roughly three#$uarters water, prevents the ends of these

bones from grinding against each other as you moveO instead the bone ends simply glide across

each other with very little friction. =artilage also absorbs the shock of movement. This is

particularly important to the knee, a weight#bearing joint that is subject to constant poundingD as

every time you step and your foot hits the ground, shock waves reverberate up your leg bones.

When walking, the stress on your knee is roughly three times your body weight, a figure that

increases to ten times your body weight when you run. Without cartilage, the impact of

movement would cause stress fractures of the bones, erosion of bone ends, the formation of bone

spurs Bthink calluses on the ends of the bonesC, and ultimately the destruction of both the bones

and the weight#bearing joints.

)ecause the knee is subject to so much stress, a thick layer of cartilaginous tissue called the

meniscus Bplural menisciC cushions the ends of the femur and the tibia. The meniscus is an

excellent shock absorber, soaking up the impact created by movement and helping 8nee muscle,

arthritis of the knee provide stability to the knee joint. damaged meniscus, which is common

ig &.+D 8nee joint showing the cartilage and the menicus


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among athletes participating in contact sports, is often referred to as Ptorn cartilage.P nother

kind of cartilage found in the knee joint is articular cartilage, the PstandardP kind thatNs found in

most joints. This smooth, slick surface covers the underside of the patella and lines the femoral

groove allowing these bones to glide smoothly within the joint as the knee bends and straightens.

When either kind of cartilage within the knee becomes cracked, torn, thin, dried out or worn

through, its ability to absorb shock and cushion the bone ends is reduced. 8nee bones begin to

grind against each other, causing pain, stiffness, loss of movement and sometimes swelling # in

other words, a condition called arthritis. nd that can really put a damper on your life.


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#.#." Derees of Free2om

The type of joint in the knee is a hinge joint BginglymusC in which the articular surfaces are

molded to each other in such a manner as to permit motion only in one plane. In this case, the

plane is the lexion#extension plane about the sagittal axis.

#.#.# 5)as(!st(ffness of Knee

ig &.0D >arious dimensional motions of 8neeF&3G

a A moment when heel strikes the

ground

b A maximum moment at an angle of (1

c A moment when the leg is at the end

of weight acceptance phase

d A moment at terminal stance phase

e A moment at swing phase

ig. &.1D "oment#ngle 5raph F&G


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)iomechanical data characterizing the $uasi#stiffness of lower#limb joints during human

locomotion is limited. Hnderstanding joint stiffness is critical for evaluating gait function and

designing devices such as prostheses and orthoses intended to emulate biological properties of

human legs. The knee joint moment#angle relationship is approximately linear in the flexion and

extension stages of stance, exhibiting nearly constant stiffnesses, known as the $uasi#stiffnesses

of each stage. "echanisms that can emulate human#like biomechanics areessential for robust

performance of a number of engineered locomotion systems including anthropomorphic bipedal

robots, lower#limb wearable exoskeletons, and biologicallyinspired prosthetic limbs. Ideally,

successful emulation ofhuman locomotion in artificial systems is built upon a foundationof

simple models Btheoretical or empiricalC that can accurately characterize the normal mechanical

behavior of the human limb during gait.

The $uasi#stiffness is defined as the stiffness of a spring that best mimics the overall behavior

of a joint during a locomotion task. It can be estimated using the slope of the best linear fit on the

moment#angle graph of the joint. The $uasi#stiffness of a joint explains how a joint functions

during a locomotion task or phase, distinguishing it from the passive and active stiffness of a

joint defined as a specific function of angle and time. The concept of $uasi#stiffness applies

particularly well to the knee joint during stance phase of walking, where a substantial moment is

applied to compliantly support the body weight. This compliance was originally considered a

determinant factor in reducing the vertical travel of center of gravity of the body, and later shown

to play a major role in shock absorption. pplying a preliminary $uasistiffness analysis revealed

a nearly linear spring#like behavior that changes with both gait speed and load carriage. Indeed, a

simple spring#like approximation of knee performance leads to much simpler mechanical designs

of assistive devices, leading to greater robustness, lower cost, lighter weight, and higher shock

tolerance. rom the experimental side, it is possible to characterize the kinetic and kinematic

behavior of the joints using data captured from humans in a gait laboratory. The characteristic

stiffness of the knee in flexion and extension modes are nearly identical at preferred walking

speed and differ as the gait speed deviates from the natural value. The variations of the

characteristic stiffness of the knee has two implications for the design of stance control orthoses.

irst, the knee does not exhibit a single characteristic stiffness for all walking speeds. s shown

earlier, the characteristic stiffness of the knee changes as the gait speed varies. In an ideal case,


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the design of a parallel assistive device for a wide range of walking speeds would implement a

variable stiffness mechanism to allow the characteristic stiffness of the knee in the flexion mode

to increase and in the extension mode to decrease, with some added damping, as the walking

speed increases. Jowever, creating a truly variable stiffness mechanism is challenging in

practice. lternatively, the design of assistive devices and bipedal robots might implement a

spring with the stiffness that is some weighted average of the expected range of gait %peeds. In

addition to the stiffness, the overall knee flexion and extension, zero moment angle, and

maximum moment also change with gait speed. The amount of rotation of the knee linearly

increases Bfor the flexion mode and for the extension modeC as gait speed increases. Therefore,

the design of assistive devices should allow for greater rotation when the user walks faster.

#.#.$ Loa2 *onstra(nts on the /nee

The maximum tibiofemoral compressive force reached an average load of +.< times body#

weight B)WC for level walking and ; times )W for downhill walking, in each instance during the

early stance phase. "uscle forces contributed ;'@ of the maximum bone#on#bone force during

downhill walking and 4'@ during level walking whereas the ground reaction forces contributed

only &'@ and +'@ respectively.

"ost total knee designs provide a tibiofemoral contact area of ('' to +'' mm&. The yield

point of these polyethylene inlays will therefore be exceeded with each step during downhill

walking. uture evaluation of total knee designs should be based on a tibiofemoral joint load of

+.1 times )W at &'M knee.

The highest knee joint loadings occurred during downhill walking. The peak joint moments

occurred at 0( Q 3M knee flexion and were &.41 Q '.1 *m?kg for females and &.4' Q '.4 *m?kg

for males. The vertical joint reaction forces were (1.& Q (.3 *?kg for females and (1.1 Q (.arious materials for fabrication of a 82 include but are not limited to

metals, plastics, fabrics, and leather. =onditions that might benefit from the use of a 82

include paralysis, joint laxity or arthritis, fracture, and others. lthough not as widely used as

knee orthoses, 82s can make a real difference in the life of a paralyzed person, helping them

to walk therapeutically or, in the case of polio patients on a community level. These devices are

expensive and re$uire maintenance. %ome research is being done to enhance the design, even

*% helped spearhead the development of a special knee joint for 82s


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Traditionally, the affected knee is supported during walking using a kneeEankleEfoot orthosis

B82C, comprising a rigid thermoplastic cast formed around the impaired leg. Traditional

82 lock the knees throughout the gait cycle therefore demands compensatory, unnatural, and

metabolically expensive movements from the wearer.

%tance control 82s B%=82sC have recently been commercialized and used clinically

for patients with paresis and paralysis in the lower limb muscles. Hnlike traditional 82s,

%=82s actively lock the knee only during the stance phase and allow for free rotation during

the swing phase. This improvement has led to many medical benefits, including increased

walking speed, knee range of motion, stride, step lengths, user satisfaction, reduced energy

expenditure and gait asymmetry, as well as kinematic benefits to both affected and unaffected

legs, compared with regular 82s. Jowever, rigid locking of the knee joint during stance

phase in current %=82s hinders the shock absorbing flexion of the knee, and can potentially

cause increased metabolic cost, user pain and discomfort and limited gait speed.

#.$." T4pes of E1os/eletons

The exoskeletons are of two typesD

Parallel t4pe6

Increases %trength

-oad =arrying

Jigh#g 5aits 7nergy !ecovery

6ower ssist

=ontrollability

Hser orce is directly effective

5ives 6osition feedback to user

6assive assist re$uires disengagement to allow foot lift 7xoskeleton assist adds orce

ig. &.3D 6arallel type F(1G


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Ser(es T4pe6

Increases 7xtension

%hock !eduction 7nergy !ecovery

6ossible Increased 9oint %tress

=ontrollability

Hser "otion is directly effective 6assive ssist can cause foot dragging, interfere with normal gait

5ives direct orce feedback to user

ctive assist adds "otion

or the current project, the parallel type of exoskeleton will be used which is ideal for our

usage in the case of load carrying and power assisted usage in the form of support of knees.

i . &.4D %eries T e (1


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C+APTER $

PRESENT IN-ESTIGATION

$." 0oment Anle beha3(or of Knee

ig.+.( schematically depicts the lower extremity limbs in a gait cycle, and ig. +.bottom

shows a typical moment#angle cycle for an unimpaired knee during walking on level ground,

ig. +.(D -ower 7xtremity -imbs

ig. +.&D "oment#ngle =ycle for unimpaired knee


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with the corresponding gait instants labeled. The stance phase of walking is composed of a

weight acceptance phase Ffirst 0'@, as depicted in ig. &BaCEBcCG and a stance termination phase

F0'@E3+@, as shown in ig. &BcC and BdCG. :uring the weight acceptance phase, the knee

undergoes substantial loads to support the weight of the superior limbsO therefore, it is highly

prone to collapse without proper function of the musculature system or external assistance during

this phase. s ig. & shows and previous research suggests, the knee behaves close to a linear

torsional spring in the weight#acceptance phase Bparticularly at the preferred gait speedC. This

spring stiffness is defined as the slope of a linear fit to the moment angle graph of the knee in this

phase.

ig. &. TopD %chematic of lower extremity limbs during a gait cycle. 8nee behaves close to a

torsional spring in the weight acceptance phase of the gait as indicated. )ottomD "oment#angle

graph for the knee of a subject walking at (.&1. %lope of the linear fit to the graph in the weight

acceptance phase is termed as the knee $uasi#stiffness in this phase. 8nee function can be

replaced by a linear torsional spring with spring constant e$ual to the knee $uasi#stiffness. The

knee exhibits substantially smaller $uasi#stiffness and moment during the terminal stance phase

and remains nearly silent during the swing phase of the gaitO implying a less eminent need for

external stabilization. In our previous work, we investigated the linear moment# angle behavior

of the lower extremity joints.

$.# Des(n Ob7e*t(3es

In order to approximate the linear moment# angle behavior of the knee, a compliant knee

joint should engage a linear torsional spring in parallel with the knee at the onset of the stance

phase and disengage it at the end of the weight acceptance phase to allow for free motion during

the rest of the gait. =onsidering the biological performance of the human knee explained in the

previous section and extensive consultation we received from orthotists, we envision the

following functional and safety re$uirements for the designed exoskeletonD

(. The knee joint stiffness of the mechanism, in stance, should be sizable selectable

for a specific user depending on stature and gait conditions.


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&. The mechanism should be capable of accommodating torsional stiffness of ;'E

41' and maximum moment of up to ('1 *.m.+. The mechanism should provide fast switching between the weight acceptance and

the rest of the gait cycle based on the input of the sensors in the insole.

0. The mechanism should fit a range of individuals of various height, weight andgait patterns.

$.$ Des*r(pt(on of the total s4stemThe 7xoskeleton basically consists of 1 elementsD

(. uick !eturn "echanism

&. :ouble Torsion %pring+. %ensors

0. "otor

1. "icro =ontroller

The total system consists of a double torsion spring in parallel with the knee providing the

re$uired stiffness during the different phases of the gait cycle. The double torsion spring is

controlled by a =ontrol module consisting of a Whitworth uick !eturn "echanism connected

to the spring by a string. The speed of the =ontrol module are regulated by the sensors placed in

the insole of the shoe which gives the starting and end of the stance cycle of the user. The total

system is integrated into a regular 82 that lacks a lateral knee joint.

The lateral joint of the system is primarily composed of a thigh chassis and a shank chassis as

well as a pulley and additional structural components. The =ontrol module is assembled on the

thigh and the spring on the shank chassis.

7xoskeleton -eg ttachment can be represented as followsD


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ig.+.0BaCD 7xoskeleton -eg ttachment &

ig.+.+D 7xoskeleton -eg ttachment (


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$.$." Control 0o2)le

The control module consists of a Whitworth uick !eturn "echanism which controls the

stiffening and the loosening of the torsion spring. The "echanism is designed to withstand the

load of the maximum moment of ('1 *.m re$uired during the gait cycle and provide a cyclic

stiffening and loosening of the torsion spring to go with the stance and swing cycle of the gait.

*ecessary calculations have been done to design and simulate the Whitworth uick return

mechanism.

$.$.# 5)(*/ Ret)rn 0e*han(sm

$uick return mechanism is a mechanism that converts rotary motion into reciprocating

motion at different rate for its two strokes. When the time re$uired for the working stroke is

greater than that of the return stroke, it is a $uick return mechanism.

This mechanism is made of a driving crank and of a driven slider crank. In the considered

configuration, the fixed pivot of the driven crank is located on the outside of the circle on which

the end of the driving crank moves. This leads to an alternated motion of the slider crank. The

configuration where this pivot is located inside the circle on which the end of the driving crankmoves. The angular speed of the driven crank is variable.

The duration of the motion for its part corresponding to the lower arc is shorter than the one

related to the upper arc. This is why this device is named $uick return mechanism, which was

used in crank shapers, with the slow part or the stroke being used for the working time of the tool

and the $uick part for the non#productive time.

The digramatical representation of different positions of Whitworth uick return mechanism

at different walking phases can be shown as below.


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:ifferent Whitworth mechanism positions at different phasesD

ig.+.0BbCD :ifferent walking positions

ig +.0BcC D :ifferent Whitworth positions at different phases


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return strock velocity +

strock velocity &work=

The link length claculations are found out as followingD

Where,

r(Alength of link connecting 2(and 2&

ig.+.1D -ink "echanism (


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r&Alength of crank

>rAmaximum return stroke velocity

>wAmaximum work stroke velocity

s slider is on same surface as point 2( in our mechanism , r4A'

or our design re$uirement we want maximum force to be at a point of extreme left. There for

calculation purpose we are considering extreme position. t extreme position crank will be

perpendicular to rockerD

r+&Ar(

r(&

r+&A&0r&

&YYY..Bfrom e$uation +.(C

r+&A& 3 r2

&

+

0

(

& 3

((.1+4('(.1+4

rTan

r

= =

=

=

s we want 1thlink to be straight with leg so that it can withstand the load.

1 (31 =

Bas the angle where we will have max stiffness is at (1oC

ig.+.3D -ink "echanism &


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*ow as per the given conditions using simple geometry,

=11.5370

&

=191.5370

ig.+.4D -ink "echanism +

ig.+.;D -ink "echanism 0


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0

0

1

1

1

sinB4;.03+C ........B C

tanB(1C01

(&.+'3

sinB(1C

(&.'3''.&1

Documents

Design of Artificial Knee Joint